Behavioral thermoregulation is highly repeatable and unaffected by digestive status in Agama atra

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Abstract

The precision and the extent of behavioral thermoregulation are likely to provide fitness benefits to ectotherms. Yet the factors driving variation in selected or preferred body temperature (Tset) and its usefulness as a proxy for optimal physiological temperature (Topt) are still debated. Although Tset is often conserved among closely related species, substantial variation at the individual, population and species level has also been reported. However, the repeatability (calculated as the intra-class correlation coefficient) of Tset is generally low. One factor that influences Tset is feeding status, with fed reptiles typically showing higher Tset, a process thought to aid meal digestion. Here, using experiments simulating realistic feeding and fasting regimes in Agama atra, a heliothermic lizard from southern Africa, we test if Tset and its repeatability under these 2 states significantly differ. Daily Tset ranged from 33.7 to 38.4 °C, with a mean (± SE) of 36.7 ± 0.1 °C for fed and 36.6 ± 0.1 °C for unfed individuals. Comparisons of repeatability showed that females tend to be more consistent in the selection of body temperature than males, but not significantly so regardless of feeding status. We report some of the highest repeatability estimates of Tset to date (full range: 0.229–0.642), and that the weak positive effects of feeding status on Tset did not increase its repeatability. In conclusion, one of the major prerequisites for natural selection, consistent
among-individual variation, is present, making the adaptive significance of Tset considerably more plausible.